The present invention is concerned with novel hydrazones of 3-formylrifamycin SV.
Certain hydrazones of 3-formylrifamycin SV are described in U.S. Pat. No. 3,342,810. These compounds, although possessing a good antibacterial activity, have practically no effect against bacteria which have become resistant to other rifamycins, namely, the well known and therapeutically useful 3-(4-methyl-1-piperazinyl-iminomethyl) rifamycin SV (rifampicin).
It is well known by those who are skilled in the antibiotic art that when a microorganism strain becomes resistant to a particular antibiotic, it is rather difficult to find another compound of the same antibiotic family which is capable of inhibiting the growth of said resistant mutant. In some instances, it is quite difficult to find compounds which are active against such a resistant strain even among other different species of antibiotics.
We have surprisingly found that representative compounds of this invention are able to inhibit at low concentration the growth of strains resistant to other rifamycins. In particular, compounds illustrative of the invention at concentrations of about 10 to 20 .mu.g/ml or less inhibit the growth of a Staph. aureus Tour strain resistant to rifampicin.